In theory, producing aggregates is a simple process, especially now that modern machines take much of the hard labour out of quarrying the aggregate. But in practice it is a much more complex process as customers require standard sized aggregates for a variety of essential uses.
Step one - Supply source:
The type of manufacturing process varies considerably depending on the source of aggregates: whether it is:
- Solid rock, such as limestone or granite;
- Loose, alluvial aggregates such as former river beds comprising sand and gravels; or
- Marine aggregates, obtained from the sea bed.
Vital materials - operating hand-in-hand with local communities
A typical hard rock quarry may last 30+ years, while sand and gravel quarries tend to be more dynamic and last a shorter time. |
Step two: extraction of the aggregate:
The extraction of the aggregates takes on very different forms depending upon the source of the material.
- Solid aggregates, such as limestone or granite, is blasted from the quarry face in highly controlled explosions managed by trained employees. This blast creates a stockpile of aggregate for processing. At Lafarge's Dowlow quarry, in the Peak District, blasting takes place roughly once a week.
- Alluvial aggregates, such as sands and gravels, are dug from the ground often using hydraulic excavators. These types of aggregates generally occur is much shallower natural deposits - sometimes of only a few metres deep. The aggregate is then loaded onto a truck or conveyor and transported to the processing plant. |
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Step three: processing - crushing, grinding, washing and screening:
Once extracted, the materials are transported to the processing plant. Here the materials pass through a series of crushers, in the case of solid rocks, the process being repeated as many times as necessary to obtain the desired fragment size.
The resulting material then passes through a series of various size screens to obtain aggregates of the desired grade/size. The larger pieces that are rejected are returned to the crusher and subsequently re-screened, with the process continuing until the desired size is obtained.
Some categories of aggregates such as sand and gravel undergo complementary processing including washing and scrubbing, primarily to make them cleaner before being stockpiled to go on to their end use. |
Sand and gravel passing through the high-pressure washing and screening plant |
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Step four: end use and land restoration:
After processing aggregates are transported for use as an end product, such as in landscaping as a decorative aggregate, for use in road bases, or as track ballast. 90% of UK aggregates are used as a raw material in the construction industry, for example in the manufacture of concrete.
Lafarge transports more of its aggregate materials by rail or barge than any other UK manufacturer and has an extensive network of rail hubs around the UK.
The land used for quarrying, is gradually restored, according to a carefully designed plan. It can be restored to create nature reserves, country parks, leisure amenities or returned to its prior use. |
A restored quarry used for boating, leisure use and as a country park. |
